By JOHN TIERNEY

Published: February 2, 1992

The Democratic Presidential candidates tried something a little uncharacteristic in their debate Friday night: deregulation. It was their third debate on national television and their first without any rules -- no fixed rotation of questions, no time limits on answers, no formal closing statements. It worked remarkably well.

The discussion sometimes wandered or got bogged down in bureaucratese, but the candidates' personalities and philosophies emerged as they bickered about infrastructure, capital gains taxes and health care plans. Unlike so many debates, this one left a television viewer with a sense of what distinguished each candidate.

It might have also left a viewer wishing that the moderators, Robert MacNeil and Jim Lehrer, were running for President. They were the sensible ones, worrying about unpleasant realities like money, and their approach was persistent without being overbearing. In a break with the traditional practice for journalists and candidates at debates, they were more interested in exploring issues than in demonstrating how smart they were.

The notion of limiting imports of Japanese cars was praised by Senator Tom Harkin of Iowa and Senator Bob Kerrey of Nebraska. They and Gov. Bill Clinton of Arkansas said that the Federal Government should rescue basic industries like steel. Edmund G. Brown Jr., the former Governor of California, wanted a complete overhaul of the tax code. Paul E. Tsongas, the former Senator from Massachusetts, talked of laws to encourage the formation of venture capital. More Authority for Tsongas

Mr. Tsongas seemed more confident after his recent gains in public opinion polls. As in previous debates, he presented himself as the candidate with integrity, the unglamorous one who would not try to buy votes with tax cuts and expensive new programs, and this time his voice did not sound quite so much like Elmer Fudd's. Although still clearly the least telegenic of the candidates, he was speaking with more authority and more succinctness.

"I'm not running to give people benefits and giveaways and lollipops that this country in terrible debt simply cannot afford," he said.

"There is no principle George Bush is not willing to sabotage for his own benefit," Mr. Tsongas said. His denunciation of Mr. Bush's character, coupled with an account of the lessons he had learned in his own battle with cancer, made for an effective, heartfelt plea. And despite occasional moments during the debate when his confidence bordered on the imperious, Mr. Tsongas was generally likable.

Mr. Kerrey was generally not. He petulantly lashed out at Mr. Clinton early in the debate, and he delivered most of his opinions in a monotonic shout. This sort of aggressiveness might impress some voters, but it seemed more suited to a rally than to a round-table debate. In a two-hour discussion on television, politeness counts for a lot.

Although most of the candidates seemed uncomfortable when asked what sort of pain would be required to pay for their new programs, Mr. Kerrey admitted to wanting new taxes to pay for his national health care plan, and he even mentioned that unpopular word, deficit.

"We've been borrowing and using a credit card to buy everything that we want," he said, criticizing the policies of the 1980's. "We're borrowing more than we should, and we've got to get that deficit under control."

Mr. Kerrey's proposed taxes were criticized by Mr. Harkin, who promised national health care, as well as a "new New Deal" to build highways and bridges, without much financial pain.

"We don't have to spend any more and we don't have to tax any more," Mr. Harkin said. "What we have to do is reshape the health care system." All America had to do, he said, was "squeeze out the waste" and "cut the administrative costs" and "reduce unnecessary medical procedures." Unfortunately, he did not specify how he hoped to do this.

His vagueness on finances was not reassuring, but at least Mr. Harkin spoke well, leaving no doubt where he stood philosophically: a good old-fashioned liberal. And toward the end of the debate, when he talked about his childhood and the problems faced by his disabled brother, he left no doubt that he believed what he was saying.

Mr. Clinton, as usual, was the unruffled man with the numbers and point-by-point plans, and he may have overdone it slightly. One of his great gifts is his ability to stop himself just as he starts to sound too smooth -- to throw in something spontaneous in the midst of a rehearsed speech, to slip a down-home example into a welter of jargon. But on Friday he sometimes got lost in the details.

"I believe in infrastructure," he said emphatically. He proposed a "comprehensive lifetime labor-market continuing-education policy." Some of Mr. Clinton's better moments were his spontaneous defenses against attacks from the rivals trailing him in the polls.

Mr. Brown summed up his opponents' ambitious proposals nicely: "This arithmetic by the end of the two hours is not going to add up." He kept talking about the "unreality" of the discussion, and at the end of the debate he brought up the topic everyone had avoided: recent accusations in a tabloid newspaper about Mr. Clinton's personal life.

A voice was heard objecting, and it turned out to be Mr. Kerrey, in perhaps his finest moment of the night, as he rose to Mr. Clinton's defense. He said the candidates should stick to the issues, which seemed an appropriate way to end an unusually substantive debate.

David S. Birdsell, the co-author of a history of political debating, said it was one of the best he had ever seen.

"There have been other debates that have had more scintillating moments," said Dr. Birdsell, a professor of speech at Baruch College and co-author of "Presidential Debates" (Oxford University Press, 1988), "but there have been few that sustained this level of substance and interest. It was consistently revealing. The stakes are getting higher, and we're seeing a little more character coming through."